1. Field of the Invention
The invention relates to a method of outputting images in digital copying machines in which image data obtained by reading a document is temporarily stored and then printed on a recording sheet while read in a desired sequence.
2. Discussion of the Related Art
Ordinary electrophotographic copying machines (hereinafter referred to as "light-lens type electrophotographic copying machines") focus light reflected from a document on a photoreceptor using a lens to expose the photoreceptor and form latent electrostatic images thereon. The latent electrostatic images are then developed and formed into a toner image, and this toner image is then transferred onto a recording sheet thereby to produce a copy of the document.
A new type of electrophotographic copying machine, which is generally called a "digital copying machine," is attracting much attention. These digital copying machines operate by reading the image of a document (using, for example, an image-sensor-based image input unit) to obtain image signals, converting the obtained image signals into digital signals, processing the digitized image signals, and then forming the image corresponding to the document on a recording sheet using an image output unit such as a laser printer.
The digital copying machine processes image signals from the image input unit almost in real time and feeds the processed signals to the image output unit.
To increase the copying efficiency, the digital copying machine is also used in combination with an automatic document handler (ADH) or a recirculating automatic document handler (RDH).
Let us not take an example in which a digital copying machine equipped with an ADH prepares n copies of a document consisting of m pages in sorted form. Copying with an ordinary ADH not capable of recirculating documents requires that n copies be produced successively for each page of the document and that the produced copies be discharged sequentially into n different bins using a sorter, and this operation must be repeated m times to have a set of m-paged copies sorted in each bin. Copying with an RDH, on the other hand, allows the required number of copies to be produced in sorted form without using a sorter. That is, m pages of the document are copied sequentially once and the processed copies are discharged into a discharge tray, and thereafter, the document is recirculated as many times as the required number of copies. However, in the RDH, the document must go through belts and rollers so many times that it is much more likely to be damaged.
To overcome this shortcoming, it has been proposed that all the image data of the document be once stored in a large-capacity storing unit and that the stored data be read in a desired sequence to be output to a recording sheet.
For example, all the images in m pages of a document are read by the image input unit to obtain their image signals. The obtained image signals are then converted into corresponding digital signals and stored in a hard disk unit. If the stored digital signals are repeatedly read and output from the hard disk unit in the order of first, second, third, to mth pages, and so on, the required number (n) of copies can be prepared in sorted form by reading the document only once and without using a sorter.
Further, the image output unit of the copying machine may be used as a printer for another image data source, e.g., a work station, if it is arranged so that a job can be accepted from another image data source through a communication line and applied to the image output unit during a period in which a job is being read from the image input unit and stored in the storing unit. And upon end of the job from the work station, the stored image data of the document can be read from the storing unit and applied to the image output unit thereby to produce copies.
Accordingly, the shared use of the image output unit of the copying machine contributes to not only streamlining units of similar function but also eliminating wasteful wait times. The term "job" herein used is intended to mean a block of image data which is subjected to the same processing.
The light-lens type, or analog, copying machines and many digital copying machines of the prior art have their image input unit and image output unit operated almost in real time. As a result, when an input error occurs such as a misfeed at the ADH or damage of the document scanning section, the machines are stopped after the data read up to the occurrence of the error is printed. Thus, by analyzing the copies produced up to that moment, the operator can judge where to resume the operation.
In the above-mentioned digital copying machine, the image input unit and the image output unit operate asynchronously by storing the read images. The asynchronous operation improves productivity as well as performance with an electronic RDH. However, the operator still must check the produced copies upon interruption of the copying machine due to an input error to find the last stored page of the document due to the asynchronism between the input and output operations.
Thus, to resume the copying operation when the input error has been eliminated, there has been a problem of not knowing which page of the document to re-input.